Test methods for determining leaks in empty containers has been accomplished by several methods.
In a first method, the open end of an empty container is sealed and the container is placed in a liquid. Bubbles escaping from the interior of the container indicate a leak. This process may be hastened if a positive gas pressure is applied to the interior of the container. But the pressure cannot exceed certain levels to avoid bursting the container. Also slow, very small leaks may not quickly produce an easily detectable bubble, even under pressures approaching the bursting strength of the container. While partially effective, this process is relatively slow and undesirable for high speed testing purposes.
Another method is to seal the container and place it in a chamber of pressurized fluid. Seepage through a leak will thus occur inwardly through the container and into the container interior where it may be detected by appropriate sensors. Again, the test pressure cannot be elevated beyond the bursting pressure of the container.
In still another method, the container is sealed and placed in a vacuum chamber where the atmosphere about the container is evacuated. Leaks in the container may be detected by pressure change (drop) within the container or by detectable decay of the vacuum in the outer test chamber.
Various other forms of testing processes involving one or more of the above processes or variations thereof have also been employed.
It is understood that increased test pressures will usually result in quicker detection of leaks. However, high test pressures have been avoided to prevent damage to the container. A problem has therefore remained to provide fast yet effective nondestructive leak testing for empty containers and container members.